To achieve luminous colors similar to daylight, metal halide discharge lamps generally contain thallium. By way of example, U.S. Pat. No. 6,107,742 describes a lamp which contains a metal halide fill comprising the metals Cs, Tl, and rare earths, such as Dy, Tm, Ho, and has a luminous color similar to daylight.
Moreover, U.S. Pat. No. 5,965,984 has disclosed a fill for metal halide lamps which contains In halide. The fill may additionally contain metal halides comprising the metals rare earths, such as Tm, Ho with the exception of DyI3. It is used for photo-optical purposes, i.e. for high luminous densities. In this case, the wall loading is typically 48 to 62 W/cm2, the specific power is 35 to 70 W/mm arc length, and the electrode gap is less than 5 mm, while the quantity of lnI is 0.1 to 1.5 mg/ml.
US-A 2004253897 has disclosed a metal halide lamp with a two-ended outer bulb which surrounds only part of the discharge vessel.